Apparatus for effluent treatment



0 United States Patent 1111 3,543,936

[72] inventors JamesWllllam Abson References Cited Cheadle Hulme; UNITED STATES PATENTS Erich clflkrcheadleflan 1069169 8/1913 Parker 210/44-x crayrmsleyrEnflland 1 344 127 6/1920 Greenawalt... 209/164 1 P 707,112 l:430:l82 9/1922 Peck 210/44 1 Filed Feb-21,1968 2,258,507 10/1941 Hoag 209/166 1 Patented Rec-1,1970 2,334,703 11/1943 Henkel... 210/44 1 Asslgnee slmoll-cmesumiled 3,035,992 5/1962 Hougen 204/149 CheadleflealhrsmcklwflrEngland 3,347,786 10/1967 Baeretal 2l0/61-X 32 Priority Feb. 23, 1967 I 33] Great Britain Pnmary Examiner-Michael E. Rogers [31] No. 8603/67 AltomeyHolman, Glascock, Downing & Seebold [54] APPARATUS FOR EFFLUENT TREATMENT 11 Claims, 3 Drawing Figs.

[52] U.S. Cl 210/221, 204/149,210 10,210/13 [51] Int. Cl C02c 5/12 [50] Field of Search 204/ 149,

ABSTRACT: In the treatment of effluent sludge, electrodes are immersed in the effluent sludge and a potential difference is applied and maintained across them at a low current density sufficient to cause gassing whereby a layer of thickened sludge rises to the surface of the liquor and is removed.

Patented De .1,191o' e 3,543,936

Shut I of 2 JAMES W/L L /4M 48 501V ERIC lN/VES (42K //IN MAL COL M 6E4 Y Patented Dec. 1, 1970 I She 2 o! 2 0m v -J m wE NM 3 Q Q Q ON NNQ @N S Q 2 Q E APPARATUS FOR EFFLUENT TREATMENT This invention is concerned with apparatus for and methods of treatment of effluent.

At times in the treatment of effluents for example municipal sewage and industrial effluents, sludges of high organic content are produced which frequently present a problem, arising at least in part from difficulties in reducing the water content of the sludges to thicken them.

For example, in the treatment of municipal sewage, usually the raw untreated sewage enters primary settling tanks where a sludge of high organic content is settled out; this sludge of high organic content is settled out; this sludge is then digested by the action of anaerobic bacteria and preferably before digestion the sludge is thickened. Clear liquor from the primary settling tanks passes to aeration tanks where it is treated with an activated sludge of high organic contend; the activated sludge is then settled and recycled to the aeration tanks; however surplus activated sludge is produced which is preferably thickened before disposal. 7

It is an object of the invention to provide an improved method of thickening an effluent sludge of high organic content.

According to one aspect of the present invention there is provided a method of treating effluent sludge comprising the steps of immersing electrodes in effluent sludge applying a potential difference across the electrodes at a low current density sufficient to cause gassing, maintaining the current flow so that a layer of thickened sludge is formed, and removing the layer of thickened sludge from the remainder of the liquor.

Advantageously, the method defined above is for the continuous treatment of effluent sludge and includes the steps of passing the effluent sludge continuously into the vicinity of the electrodes and removing separately and continuously the thickened sludge and the remainder of the liquor.

Advantageously, the effluent sludges is treated for an average period of from one to two and one half hours, preferably 1 to 2 hours and more preferably 1.85 hours.

The current density during treatment may be between 0.003

amp/in2 of cathode (0.00046 amp/cm2 of cathode) and 0.02 amp/in2 of cathode (0.0031 amp/cm2 of cathode), advantageously the current density is between 0.0085 amp/in2 of cathodes (0.0007 amplcm2 of cathode) and 0.01 amp/in2 of cathode (0.0015 amp/cm2 of cathode), the preferable current density being 0.007 amp/in2 of cathode (0.001 amp/cmZ of cathode).

According to a second aspect of the present invention there is provided apparatus for treating effluent sludge comprising a container, spaced electrodes located in the container and arranged to be immersed in effluent sludge, means for applying and maintaining a potential difference across the electrodes at a low current density sufficient to cause gassing and formation of a layer of thickened sludge, and means for removing the layer of thickened sludge from the remainder of the liquor.

The electrodes may comprise an aluminum cathode and at least one anode containing iron.

Alternatively, the electrodes may be of carbon,

Conveniently the initial solids content of the sludge immediately prior to treatment by the method is not greater than 3 percent by weight. After treatment by the method the thickened sludge may have its water content further reduced by other methods.

Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a cutaway perspective view of one form of apparatus for treating effluent sludge according to the present invention.

FIG. 2 is a schematic side view of a modified form of apparatus according to the present invention and FIG. 3 is a plan view of the apparatus shown in FIG. 2.

Referring to FIG. 1 the apparatus comprises a tank 12 in which is mounted along a base 14 thereof a horizontal planar aluminum cathode 16. A plurality of vertical, parallel, planar, evenly-spaced, shallow, mild steel anodes 18 are also mounted in the tank 12. The anodes 18 are suspended above the cathode 16 by electrically conductive rods 20 which are mounted in two spaced insulated support members 22.

In the operation of the apparatus an effluent sludge of high organic content is pumped continuously into the tank 12 along a line 24 and a potential difference at a low current density applied between the anodes 18 and the cathode 16 causes separation and sludge and aqueous liquor; the sludge rises to the liquid surface and forms a layer which is removed by removal means (not shown); the clear liquor is pumped out of the tank 12 along a line 26. The liquid level in the tank 12 is near the top of the tank 12 well above the anodes 18.

The apparatus may also be used under batch conditions instead of continuous flow conditions.

The space between adjacent anodes is preferably between 0.05 inches (1.27 cm) and 2 inches (5.08 cm) and the distance between the cathode and the bottom edges of the anodes is preferably between 0.25 inches (0.635 cm) and 1 inch (2.54 cm).

It is believed that the action of the potential difference involves flocculation promoted by hydroxyl ions, the flocs being carried to the liquid surface by gas bubbles produced by electrolysis.

Examples of methods of treating effluent sludge in the apparatus shown in FIG. 1 will now be described.

EXAMPLE 1 The apparatus described with reference to the drawings was used with the following parameters:

Cathode: 22.5 inches (57.2 cm) X 11.38 inches (28.9 em) 256 in. 2 (1655 cm 2 Anodes: each 11.375 inches X 1.5 inches= 17 in. 2 cm Distance between cathode and bottom edges of anodes: 0.75 inches (1.9 cm) Voltage: 8.6 volts. Current: 4 amps.

Current density: 0.016 amps. per square inch'of cathode (0.0024 amp/cm 2 cathode). I

Capacity of tank: 8 gallons (36 litres).

An activated sludge derived from the treatment of municipal sewage was treated in the apparatus under batch conditions for 2 hours. The initial solids content of the sludge before treatment in the apparatus was 0.81 percent by weight and the final solids content after treatment was 4.23 percent by weight.

EXAMPLE 11 EXAMPLE m The apparatus described with reference to the drawings was used with the same parameters in Example 1.

An activated sludge derived from the treatment of municipal sewage was treated in the apparatus under batch conditions for 2 hours. The initial solids content of the sludge was 0.83 percent by weight and the final solids content was 3.98 percent by weight.

EXAMPLE IV The apparatus described with reference to the drawing was used to treat, for half an hour under batch conditions, a raw municipal sewage sludge from primary settling tanks; the voltof the container and being spaced above the bottom ofthe container so as to define a passage which directs the effluent liquor from the inlet means between the electrodes, means for applying and maintaining a potential difference across the electrodes at a low current density sufficient to cause gassing and formation of a layer of thickened organic solids, and an inclined conveyor disposed at the opposite end of th the electrodes to the inlet means, the lower end of the conveyor, in use, being immersed in the effluent liquor so that the thickened organic solids can be continuously removed from the container.

2. Apparatus as claimed in claim I, wherein an outlet is provided below the inclined conveyor for removing continuously the remainder of the effluent liquor, from which thickened organic solids have been removed, the outlet being disposed across the width of the container.

3. Apparatus as claimed in claim 1, wherein the electrodes comprise a cathode in the form of a plate in the base of the container and at least one anode spaced above the cathode.

4. Apparatus as claimed in claim 3, wherein the anode is in the form of a plurality of spaced. plates connected together and supported on electrically conductive rods.

5. Apparatus as claimed in claim 3 wherein the spacing between the cathode and anode is in the range 0.25 l inch (0.635 254 cm.).

6. Apparatus as claimed in claim 3 wherein the cathode is of aluminum and the or each anode contains iron.

7. Apparatus as claimed in claim 1 wherein the electrodes are of carbon.

8. Apparatus as claim in claim 1 wherein the electrodes are of graphite.

9. Apparatus as claimed in claim 1 for the continuous treatment of effluent sludge, wherein there is provided an inlet through which effluent sludge can be continuously introduced into the container, an outlet by means of which the said remainder of the liquor can be continuously removed from the container, and continuously operable means for removing the layer of thickened sludge from the remainder of the liquor.

10. Apparatus as claimed in claim 9, wherein the continuously operable means is a continuous conveyor.

11. Apparatus as claimed in claim 9 wherein the inlet is adapted to allow effluent sludge to be introduced into one end of the container across the width thereof and the outlet is arranged to allow the said remainder of the liquor to be removed from the other end of the container across the width thereof. 

